1. Field of the Invention
This invention relates generally to a clutch mechanism of an automatic washing machine for transmitting power of a drive motor selectively to an agitator in a wash step and a rotatable tub and the agitator in a dehydration step, and more particularly to such a clutch mechanism wherein buoyancy of water is utilized for switching transmission of motor power between the wash and dehydration steps.
2. Description of the Prior Art
Automatic washing machines have conventionally been provided with a single electric motor driven in common for a washing operation and a dehydrating or spin drying operation. Power of the motor is transmitted to an agitator provided in a rotatable tub so that the agitator is driven in a wash step. On the other hand, the motor power is transmitted both to the agitator and to the rotatable tub so that they are driven in a dehydration step. A clutch mechanism has been employed for switching the transmission of the motor power between the wash and dehydration steps. The clutch mechanism conventionally comprises clutch springs provided in the midway of a power transmission path between the motor and the agitator and rotatable tub.
Each clutch spring employed in the above-described clutch mechanism requires high precision in its number of turns, its inner diameter and the like. Furthermore, electromagnets and an electric motor are required for controlling the movement of the clutch springs. Consequently, the conventional clutch mechanism has a complicate construction, resulting in increase in the manufacturing cost.
In view of the above-described problem, publication Nos. 57-103690 and 62-268343 of Japanese unexamined patent applications disclose improved automatic washing machines. In these automatic washing machines, a float chamber is formed on a bottom underside of a rotatable tub. The rotatable tub has a power receiving section which is usually engaged with a power transmitting member mounted together with the agitator on a shaft driven by a drive motor. Water is supplied into the rotatable tub in the wash step so that the water is reserved in the rotatable tub and an outer non-rotatable tub enclosing the former. The rotatable tub is caused to move upwardly when the float chamber is filled by air. Consequently, the power receiving section is disengaged from the power transmitting member such that the motor power is transmitted via the shaft only to the agitator but not to the rotatable tub. In the dehydration step, the water is discharged out of the rotatable and non-rotatable tubs. The rotatable tub is caused to move downwardly as the result of disappearance of the buoyancy such that the power receiving section thereof is re-engaged with the power transmitting member. Consequently, the motor power is transmitted via the shaft both to the agitator and to the rotatable tub in the dehydration step. The above-described power transmitting mechanism has a simple construction and does not require high precision for the parts, whereupon the washing machines can be manufactured at a low cost.
In the above-described construction, however, a space needs to be provided over the rotatable tub to allow the same to move upwardly in the wash step. There is a possibility that the laundry may be caused to scatter through the space out of the washing machine in the dehydration step where the rotatable tub is caused to move downwardly. Furthermore, the space increases the height of the washing machine, which makes it difficult for a user to take the laundry out of the rotatable tub. Additionally, the rotatable tub is sometimes inclined when lowering. When the motor power is transmitted to the inclined rotatable tub, it is swayed in the dehydration step, causing abnormal vibration.